In 3GPP (3rd Generation Partnership Project) that is a standardization project of a mobile communication system, as a new feature of release 12 or later, introduction of Device to Device (D2D) communication has been considered (see Non Patent Literature 1).
In D2D communication, a plurality of user terminals that is adjacent to each other perform direct device to device communication without going through a network. On the other hand, in cellular communication that is normal communication of the mobile communication system, the user terminals perform communication through the network.